Retrocausality

Source: Wikipedia, the free encyclopedia.

Retrocausality, or backwards causation, is a concept of

quantum physics, the distinction between cause and effect is not made at the most fundamental level and so time-symmetric systems can be viewed as causal or retrocausal.[3][page needed] Philosophical considerations of time travel often address the same issues as retrocausality, as do treatments of the subject in fiction, but the two phenomena are distinct.[1]

Philosophy

See also: Principle of sufficient reason § Proposed proofs of universal validity

Philosophical efforts to understand causality extend back at least to Aristotle's discussions of the four causes. It was long considered that an effect preceding its cause is an inherent self-contradiction because, as 18th century philosopher David Hume discussed, when examining two related events, the cause is by definition the one that precedes the effect.[4][page needed]

In the 1950s,

Essentialist philosophers have proposed other theories, such as the existence of "genuine causal powers in nature" or by raising concerns about the role of induction in theories of causality.[7][page needed][8][page needed
]

Physics

Most physical theories are

Newton's laws or electromagnetism have no inherent direction of time. The "arrow of time" that distinguishes cause and effect must have another origin.[9]: 116  To reduce confusion, physicists distinguish strong (macroscopic) from weak (microscopic) causality.[10]

Macroscopic causality

The imaginary ability to affect the past is sometimes taken to suggest that causes could be negated by their own effects, creating a logical contradiction such as the

grandfather paradox.[11] This contradiction is not necessarily inherent to retrocausality or time travel; by limiting the initial conditions of time travel with consistency constraints, such paradoxes and others are avoided.[12]

Aspects of modern physics, such as the hypothetical tachyon particle and certain time-independent aspects of quantum mechanics, may allow particles or information to travel backward in time. Logical objections to macroscopic time travel may not necessarily prevent retrocausality at other scales of interaction.[13][page needed] Even if such effects are possible, however, they may not be capable of producing effects different from those that would have resulted from normal causal relationships.[14][page needed]

Physicist John G. Cramer has explored various proposed methods for nonlocal or retrocausal quantum communication and found them all flawed and, consistent with the no communication theorem, unable to transmit nonlocal signals.[15]

Relativity

cosmic strings, may allow their formation, implying a theoretical possibility of retrocausality. The exotic matter or topological defects required for the creation of those environments have not been observed.[16][page needed][17][page needed] Furthermore, the chronology protection conjecture of Stephen Hawking suggests that any such closed timelike curve would be destroyed before it could be used.[18]

Microscopic causality

Most physical models are time symmetric;[9]: 116  some use retrocausality at the microscopic level.

Electromagnetism

destructive interference to explain the absence of a type of converging concentric wave suggested by certain solutions to Maxwell's equations.[19] These advanced waves have nothing to do with cause and effect: they are simply a different mathematical way to describe normal waves. The reason they were proposed is that a charged particle would not have to act on itself, which, in normal classical electromagnetism, leads to an infinite self-force.[19]

Quantum physics

Time runs left to right in this Feynman diagram of electron–positron annihilation. When interpreted to include retrocausality, the electron (marked e−) was not destroyed, instead becoming the positron (e+) and moving backward in time.

anti-particles is required in modern quantum field theory, and is for example a component of how nucleons in atoms are held together with the nuclear force, via exchange of virtual mesons such as the pion. A meson is made up by an equal number of normal quarks and anti-quarks, and is thus simultaneously both emitted and absorbed.[21] Wheeler invoked this time-reversal concept to explain the identical properties shared by all electrons, suggesting that "they are all the same electron" with a complex, self-intersecting world line.[22] Yoichiro Nambu later applied it to all production and annihilation of particle-antiparticle pairs, stating that "the eventual creation and annihilation of pairs that may occur now and then is no creation or annihilation, but only a change of direction of moving particles, from past to future, or from future to past."[23] The backwards-in-time point of view is nowadays accepted as completely equivalent to other pictures,[24]
but it has nothing to do with the macroscopic terms "cause" and "effect", which do not appear in a microscopic physical description.

Retrocausality is associated with the Double Inferential state-Vector Formalism (DIVF), later known as the two-state vector formalism (TSVF) in quantum mechanics, where the present is characterised by quantum states of the past and the future taken in combination.[25][26]

Retrocausality is sometimes associated with the

delayed choice quantum eraser.[27][28] However accounts of quantum entanglement can be given which do not involve retrocausality. They treat the experiments demonstrating these correlations as being described from different reference frames that disagree on which measurement is a "cause" versus an "effect", as necessary to be consistent with special relativity.[29][30] That is to say, the choice of which event is the cause and which the effect is not absolute but is relative to the observer. The description of such nonlocal quantum entanglements can be described in a way that is free of retrocausality if the states of the system are considered.[31]

Tachyons

Hypothetical

Feinberg reinterpretation principle means that ordinary matter cannot be used to make a tachyon detector capable of receiving information.[32]

Parapsychology

Retrocausality is claimed to occur in some

psychokinesis.[34][35] Such results and their underlying theories have been rejected by the mainstream scientific community and are widely accepted as pseudoscience, although they continue to have some support from fringe science sources.[36][page needed][37][page needed][38][unreliable source?
]

Efforts to associate retrocausality with prayer healing have been similarly rejected.[39][40]

From 1994, psychologist Daryl J. Bem has argued for precognition. He subsequently showed experimental subjects two sets of curtains and instructed them to guess which one had a picture behind it, but did not display the picture behind the curtain until after the subject made their guess. Some results showed a higher margin of success (p. 17) for a subset of erotic images, with subjects who identified as "stimulus-seeking" in the pre-screening questionnaire scoring even higher. However, like his predecessors, his methodology has been strongly criticised and his results discounted.[41]

See also

References

  1. ^ a b Faye, Jan (2001-08-27). "Backward Causation". Stanford Encyclopedia of Philosophy. Retrieved 2006-12-24.
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  15. ^ J. G. Cramer (April 2014), "Status of Nonlocal Quantum Communication Test" (PDF), UW CENPA Annual Report 2013-14, Article 7.1, retrieved September 21, 2016
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  22. ^ Feynman, Richard (1965-12-11). The Development of the Space-Time View of Quantum Electrodynamics (Speech). Nobel Lecture. Retrieved 2007-01-02.
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  26. ^ Aharonov, Yakir & Lev Vaidman. "The Two-State Vector Formalism: An Updated Review" (PDF). Retrieved 2014-07-07.
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  29. ^ Costa de Beauregard, Olivier (1977). "Time Symmetry and the Einstein Paradox" (PDF). Il Nuovo Cimento (42B).
  30. ^ David Ellerman (2012-12-11). "A Common Fallacy in Quantum Mechanics: Why Delayed Choice Experiments do NOT imply Retrocausality". Archived from the original on 2013-06-15. Retrieved 2017-05-12.
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  33. ^ John Gribbin; Book Review of "An Experiment with Time", New Scientist, 27 Aug 1981, 548.
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  38. ^ Shoup, Richard (2002). "Anomalies and constraints: can clairvoyance, precognition, and psychokinesis be accommodated with known physics?". Journal of Scientific Exploration. 16.
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